Classical conditioning, decay and extinction of cocaine-induced hyperactivity and stereotypy

Following 10 daily pairings of multiple conditioned stimuli with injection of cocaine (15 mg/kg), the presentation of the stimuli alone elicited behaviors in rats similar to those induced by cocaine. The behaviors included increased duration or frequency of rearing, sniffing, head bobbing, and horizontal locomotor activity (crossing). The level of the conditioned response for several of these behaviors approximated that induced by the drug itself. The conditioned drug effect showed decay over 15 days but little extinction during 4 daily trials. Brain concentrations of the dopamine metabolites, homovanillic acid and dihydroxyphenylacetic acid, were similar in the conditioned and pseudoconditioned control groups in both the caudate and mesolimbic areas. The behavioral results demonstrate that, in a classical conditioning paradigm, previously neutral stimuli can elicit behaviors similar to those induced by cocaine and that certain conditioned responses show time related decline. This agrees with the reported conditioning of amphetamine's behavioral effects but differs in terms of the action on brain dopamine turnover.     

Correlation between cell cycle duration and RNA content.

The metachromatic fluorochrome acridine orange was used to differentially stain DNA and RNA in Chinese hamster ovary (CHO) cells and in mitogen-stimulated human lymphocytes during their progression through the cell cycle. Green and red fluorescence of individual cells, representing cellular DNA and RNA, respectively, was measured by flow cytometry. CHO cells were synchronized by selective detachment at mitosis. Their rate of progression through G1 and subsequently through S phase correlated with the content of stainable RNA. The mean duration of the G1 phase was 5.2 hours for cells with high RNA content (highest 25 percentile population) and 8.1 hours for cells with low RNA (lowest 25 percentile). The duration of S phase was 5.9 and 7.5 hours for high- and low-RNA, 25 percentile subpopulations, respectively. Lymphocytes synchronized at the G1/S boundary by hydroxyurea or 5-fluorodeoxyuridine showed extremely high intercellular variation with respect to content of stainable RNA. After release from the block they traversed S phase at rates linearly proportional to the content of stainable RNA. The duration of S phase was five hours for cells with high RNA-, six to nine hours for cells with moderate RNA- and up to 27 hours for cells with minimal RNA-content. The data suggest that the rate of progression through the cell cycle of individual cells within a population may be correlated with the number of ribosomes per cell.     

Different sensitivity of chromatin to acid denaturation in quiescent and cycling cells as revealed by flow cytometry.

The properties of DNA in situ as reflected by its staining with acridine orange are different in quiescent nonstimulated lymphocytes as compared with interphase lymphocytes that have entered the cell cycle after stimulation by mitogens. The difference is seen after cell treatment with buffers at pH 1.5 (1.3-1.9 range) followed by staining with acridine orange at pH 2.6 (2.3-2.9). Under these conditions the red metachromatic fluorescence of the acridine orange-DNA complex is higher in quiescent cells than in the cycling lymphocytes while the orthochromatic green fluorescence is higher in the cycling, interphase cells. The results suggest that DNA in condensed chromatin of quiescent lymphocytes (as in metaphase chromosomes) is more sensitive to acid-denaturation than DNA in dispersed chromatin of the cycling interphase cells. The phenomenon is used for flow cytometric differentiation between G0 and G1 cells and between G2 and M cells. In contrast to normal lymphocytes the method applied to neoplastic cells indicates the presence of cell subpopulations with condensed chromatin but with DNA content characteristic not only of G1 but also of S and G2 cells. The possibility that these cells represent quiescent (resting) subpopulations, arrested in G1, S and/or G2, is discussed.     

Human immunodeficiency virus type 1 tropism for brain microglial cells is determined by a region of the env glycoprotein that also controls macrophage tropism.

Human immunodeficiency virus type 1 (HIV-1), the agent of AIDS, frequently infects the central nervous system. We inoculated adult human brain cultures with chimeric viruses containing parts of the env gene of a cloned primary isolate from brain tissue, HIV-1 JRFl, inserted into the cloned DNA of a T-cell-tropic strain. A chimeric virus containing the carboxy-terminal portion of HIV-1 JRFl env did not replicate in these brain tissue cultures, while a chimera expressing an env-encoded protein containing 158 amino acids of HIV-1 JRFl gp120, including the V3 loop, replicated well in brain microglial cells, as it does in blood macrophages. Infection of brain microglial cells with such a chimera was blocked by an antibody to the V3 loop of gp 120. Thus, env determinants in the region of gp120, outside the CD4-binding site and comprising the V3 loop, are critical for efficient viral binding to and/or entry into human brain microglia.     

Conformation of RNA in situ as studied by acridine orange staining and automated cytofluorometry.

Human erythroblasts which are prereticulocyte maturation stages of red blood cells were studied by light microscopic cytochemistry and electron microscopy to provide more information on the ultrastructure of the micronucleoli which are terminal stages of nucleolar changes found during maturation of these cells. As indicated by light microscopy of smeared cells, micronucleoli were virtually the only types of nucleoli present in the last stages of maturing erythroblasts, i.e., polychromatic and orthochromatic (late polychromatic) erythroblasts. Accordingly, they were not portions of the periphery of other nucleoli. Inasmuch as most of the micronucleoli exhibited characteristic segregation of nucleolar fibrillar and granular components they presumably are producing little if any preribosomal RNA, since such segregation generally reflects inhibition of nucleolar RNA synthesis.